Green silicon carbide for gem polishing
What is Green Silicon Carbide?
Hardness: Approximately 9.5 on the Mohs scale. This makes it one of the hardest abrasives available, harder than aluminum oxide (standard sandpaper) and much harder than garnet. Characteristics: Its grains are sharp, angular, and fracture easily to create new sharp edges. This makes it a very fast-cutting and aggressive abrasive. Key Difference from Black SiC: It is purer and harder than black SiC, with fewer impurities. This results in slightly sharper grains and less chance of contamination when polishing.
Best Uses in Gem Polishing: The “Grinding” and “Shaping” Stages
Slurry for Hard Materials (Primary Use): It is most often used as a loose abrasive powder mixed with water to create a slurry. This slurry is used on: Flat Laps: For pre-forming and flattening rough gem material. Grinding Wheels: Impregnated in resin-bonded wheels for cabochon and facet grinding. Tumbling (with caution): For the coarse grind stage in a rotary tumbler to shape very hard rough.
Ideal for Very Hard Gemstones: Because of its hardness, it is excellent for working with materials that are difficult to shape with softer abrasives like aluminum oxide. Excellent For: Sapphire, Ruby, Chrysoberyl, Topaz, Aquamarine, and other beryls. Good For: Agate, Jasper, Quartz, and other hard lapidary materials.
Sanding (Less Common): You can find sandpapers/micromesh pads impregnated with silicon carbide, which are excellent for wet-sanding stones between grinding and polishing stages. These are typically black SiC, but the principle is the same.
Grit Sizes and Their Purposes
Why It’s (Usually) NOT Used for the Final Polish
Grinding: Green SiC is a friable abrasive. Its particles fracture and break down as you use them. Even at very fine grits (e.g., 3000+), some of these microscopic particles will roll between the lap and the stone, creating tiny, rounded pits instead of a true, flat, reflective polish. Polishing: A true polish requires an abrasive that breaks down into an ultra-fine paste (like diamond, cerium oxide, or aluminum oxide) that can create a perfectly flat, scratch-free surface on a microscopic level. These polishes abrade the high points without digging new pits.
Recommended Abrasive Progression for a Hard Stone (e.g., Sapphire)
Shaping: Green SiC #220 or #320 slurry on a cast iron or diamond lap. Smoothing: Green SiC #600 or #1200 slurry to remove the deeper scratches. Pre-Polish: Switch to a dedicated pre-polish lap/compound (e.g., a tin lap with 15,000 grit diamond powder or 50,000 grit aluminum oxide). This step removes the fine scratches from the SiC. Final Polish: Use a specialized polish for the material (e.g., Cerium Oxide for quartz, Diamond Compound on a ceramic lap for corundum/sapphire) to achieve the brilliant, mirror-like finish.
Safety Warning: NON-NEGOTIABLE
Respirator: The dust from any abrasive, especially silicon carbide, is extremely harmful to your lungs. You MUST work with water (wet grinding/polishing) and/or use a proper respirator. Eye Protection: Always wear safety glasses or a face shield. Contamination: This is critical. Never use the same equipment (laps, tools, pots) for different grits without thoroughly cleaning them. A single piece of coarse grit from a previous stage will ruin your final polish. Have dedicated tools for each stage if possible.
